The world-wide variation in the incidence of colon cancer and the increased incidence found in migrants from low to high risk areas support the notion that environmental factors are involved in the etiology of this disease. It has been hypothesized that intestinal bacteria may be generating carcinogens or co-carcinogens from bile acid substrates. In this regard, secondary bile acids (lithocholic and deoxycholic acid) appear to be much more toxic than their primary counterparts. The overall objective of this proposed research is to delineate the role of bile acids and the intestinal microflora in colon cancer carcinogenesis. The initial goal will be to determine the level of chemical mutagens (carcinogens) in extracted feces from individual on normal "western diets" by use of the Ames assay. The second goal will be to purify and characterize by conventional biochemical techniques 7 alpha-dehydroxylase from Clostridium leptum. The final goal will be to determine the distribution of this enzyme in different intestinal bacteria.